Implantable neurological stimulation systems include a neuro stimulator and an electrical stimulation lead or leads. The implantable neurological stimulation system delivers electrical pulses to tissue, such as neurological tissue or muscle to treat a medical condition.
One such neurological stimulation system is for spinal cord stimulation (SCS) to treat chronic pain. The leads used for SCS are implanted percutaneously through a large needle inserted into the epidural space. The use of dual leads is common and most dual lead systems are implanted as two individual single lead implants. Even if the leads are implanted simultaneously, it is difficult to control the relative position of the two leads with respect to one another. In addition, there is no guarantee that the leads will not migrate or move relative to one another, thereby reducing therapy effectiveness.
There is an industry wide emphasis on maximizing neuromodulation outcomes. The selection of proper neural targets plays a significant role in achieving successful therapies using neuromodulation. Capture of these neural targets with precise electrical energy fields is a significant challenge. The target fibers within the spinal cord are arranged in such a way that is very difficult to access them with just the right amount of electrical energy. Successful neuromodulation requires delivering a balance of energy that reaches the proper neural targets without creating uncomfortable neural stimulation. This balance is particularly difficult to achieve with only one percutaneous neuro stimulator lead due to the lack of electrical field dispersion. This balance is also challenging for neuromodulation equipment that uses “single source” systems of energy. The spatial relationship between the neuromodulation equipment (the lead) and the spinal cord determine the chances of successful capture of target nerve fibers. Generating “central points of stimulation” can be very useful in achieving successful neuromodulation. Each central point of stimulation increases the odds of capturing the target nerve fibers along the spinal cord. If the neural targets along the spinal cord are located between the electrical contact points on the lead, it may be impossible to achieve successful neuromodulation. Creation of central points of stimulation depends upon the technology of the neuromodulation equipment as well as the spinal relationship and orientation of the electrode contact points on the equipment. Thus, there is tremendous benefit to optimize and secure the spatial relationship between the leads in relation to each other as well as in relation to the spinal cord itself.
The position of multiple leads relative to each other cannot be predicted or predetermined, nor maintained. This creates variability in the programming and the pattern of the field of electrical current which is generated. The vertical positioning between electrodes is imperfect as is the horizontal distance between them. both of these factors determine the shape and size of the electrical field which must be generated and optimal positioning is required otherwise programming becomes more difficult and the chances of the treatment benefiting the patient decreases.
Spinal cord stimulation makes use of different types of leads in order to effectively deliver electrical impulses to the spinal cord. These leads come in several shapes and sizes, and each has a pattern or array of electrical contact points, otherwise known as electrodes. The pattern or arrangement of the electrical contact points determine how each lead may be programmed so as to deliver varying electrical impulses. When a single lead is used the vertical arrangement of the electrode array is the primary factor that determines the size and shape of the electrical field which may be generated by opposing charges assigned to specific electrodes along the length of the lead. Leads may be positioned side by side as well. This makes it possible to create fields of current along a horizontal axis in addition to a vertical axis. Thus, the ability to position the spinal stimulator leads beside one another carries significant benefit and it provides a means to increase programming options as pertains to the arrangement of the leads once inserted into a patient. Enhanced programming options will translate into superior patient outcome with their SCS treatment.
As previously indicated, a serious problem encountered is lead migration. A percutaneous style lead is narrow and cylindrical in shape. At present, current devices which facilitate insertion of these leads beneath the skin are only capable of allowing placement of one lead at a time. Once the lead is passed beneath the skin of a patient, it is meant to reside in a specific tissue place or space, typically the epidural space next to the spinal cord. Once within the deep tissue space, because of its size and shape, the lead is highly subject to movement. The movement can occur in a vertical and/or horizontal plane. This problem happens often in the practice of medicine using SCS, and the problem is known as lead migration.
The consequence of lead migration is usually that it results in a significant change in the pattern of electrical signal generated around the spinal cord. This may create pain for a patient or render the previously useful SCS therapy worthless. A surgical revision to reposition the lead is necessary in such cases. Currently, there are anchoring devices available to tie the lead to a fixed point beneath the skin, but these have been shown to be defeatable and lead migration occurs despite their use. Leads with greater size and bulk have been manufactured to address this problem, but add discomfort and risk to the patient. Thus, their existing need to insert percutaneous SCS leads with the result that once they are inserted the possibility of their migration is reduced.
Currently it is not possible to preset or predetermine the arrangement of ones percutaneous SCS array relative to another or a multiple of others. It is also not possible to link these electrode arrays such that their vertical and horizontal inter-spacing is maintained once they are placed into a patient or subject. Furthermore, it is not possible to effectively simultaneously place pairs of multiple SCS electrode arrays into the target tissue space of the patient. A device with such capabilities so as to achieve all these goals is greatly needed.